Since 9/11, successive directors of national intelligence and C.I.A. directors were asked: “Why can’t you find Osama Bin Laden?” Their answers are summarized in 2009 by Michael McConnell, the director of national intelligence at the time: “It’s a very simple answer — because we can’t find them."

Given the enormous resources and attention required in Iraq and Afghanistan, it is unclear that finding Bin Laden was a top priority.

Eventually, however, they did find and kill Bin Laden. But why did it take so long, despite the enormous resources poured into the civilian-led intelligence community, which received $55 billion in appropriations last year, as well as support from the Pentagon?

While it is too soon to know — and the White House should release an unclassified report that explains this important intelligence success — there are several possible explanations.

First, two administrations, Congress, and the courts were — and remain — unable to find a constitutional judicial process to detain and question terrorist suspects. It is notable that the identity of Bin Laden’s courier came from intelligence extracted from terrorists operatives detained under the covert extraordinary rendition program.

After September 11, many terrorist suspects entered the program, with Pakistan having “arrested and transferred to U.S. custody nearly 500 suspected al-Qaida and Taliban terrorists,” according to the State Department’s Patterns on Global Terrorism report for 2002.

However, by 2004-2005 renditions from Pakistan ended, and the C.I.A. began targeting terrorist suspects with unmanned drones. In effect, the United States could have lost potential intelligence on Bin Laden’s whereabouts as it engaged in that effort to “degrade” or kill suspected Al Qaeda and Taliban operatives.

Second, given the enormous resources and attention required in Iraq and Afghanistan, it is unclear that finding Bin Laden was a top priority. In February 2006, a senior civilian official serving at U.S. Central Command, the military’s geographic command covering the Middle East and South Asia, told me that when he looked into this question he was disappointed to learn that given Central Command’s other commitments the Bin Laden issue was being worked (albeit persistently and professionally) at a lower level than he would have suspected.

That same year, the reporter Dana Priest revealed that President Bush felt compelled to “flood the zone” with additional intelligence officers in the region as the trail for Bin Laden had become “stone cold.” Reportedly, increased resources and a reorganized C.I.A. unit dedicated to this mission helped discover the breakthrough that led to Bin Laden.

Third, given the failure to kill Bin Laden with 66 cruise missiles in August 1998 and faulty intelligence used in the simultaneous bombing of a pharmaceutical plant in Khartoum, Sudan, policymakers were cautious about the quality of any information regarding Bin Laden. As C.I.A. director George Tenet wrote: “My job was to assess objectively whether the data we had . . . could ever get policymakers above a 50 or 60 percent confidence level so they could launch cruise missiles in the next thirty minutes. It never did.” According to C.I.A. analysts, the recent intelligence on Bin Laden’s location was assessed at 60 to 80 percent reliability, which met whatever threshold President Obama needed to authorize the helicopter raid.

Fourth, many of the assumptions held by policymakers and the public about where Bin Laden would be located were wrong. In his 2008 satirical documentary, “Where in the World is Osama Bin Laden,” director Morgan Spurlock posed that question to many Pakistanis, Afghans, and U.S. soldiers, who overwhelmingly pointed to the rough terrains and caves of North Waziristan of Pakistan’s Federally Administrated Tribal Areas.

It turns out that Bin Laden was living in a relatively luxurious compound in Abbottabad. As a senior U.S. intelligence official noted: “he was more or less hiding in plain sight.” Who would have known?